Cracks Along Plasterboard Joints And Nail Pops

What's happening?

These two faults have one cause between them: the board is moving relative to the timber it is fixed to. A plasterboard joint is a butt between two sheets, and it only holds a rigid finish because it is reinforced with scrim or jointing tape. Where the tape was omitted, laid over dust, or bridged with filler instead, the joint opens into a dead straight crack along the board edge. A nail pop is the same movement seen at a point: as the stud or joist dries and shrinks, or the board flexes, the fixing head stops being tight and the plaster over it lifts off in a small disc. Both are more common in a house's first heating season, and both are finishing faults rather than structural ones.

What usually causes it?

• Board joints not scrimmed or taped, or taped over dusty edges so the tape never bonded
• Cut board edges butted without the joint being reinforced, which is where straight cracks start
• Nails used instead of screws, or fixings driven too shallow, too deep or off the stud centre
• Timber studs or joists shrinking as the house dries out, backing away from the fixing head
• Boards fixed to timber that was wet when it was built in, so it shrank more than usual afterwards
• Dot and dab boards moving on their dabs where the adhesive coverage was thin or the wall was dusty
• Deflection or vibration in a floor or partition, working the joint every time someone crosses the room

When should you call a plasterer?

Call a plasterer where cracking runs along several joints, where the same crack has already been filled and returned, or where the surface would look better skimmed than patched. Also call where boards feel loose or drummy, since that is refixing rather than filling. Call a builder instead if the crack keeps widening month on month, or if the floor above a cracked ceiling flexes noticeably underfoot.

What will the plasterer actually do?

• Check whether the boards are properly fixed and whether the joints were reinforced before deciding on a repair
• Refix loose boards into the studs or joists with screws, replacing failed nails rather than re-driving them
• Rake out cracked joints and re-tape with scrim or mesh so the reinforcement is under the filler, not over it
• Cut back nail pops to sound material and fill in thin passes, feathered wide enough to disappear under paint
• Skim the wall or ceiling in full where cracking is widespread and patch repairs would still read through the finish
• Report progressive movement or a deflecting floor rather than filling the same line a third time